If you put an Elodea plant in a test tube containing bromothymol blue and watch the oxygen level, the time of the day in which the oxygen level in the tube would be lowest will be just before sunrise.
First, there is a need to understand oxygen is produced as a result of photosynthesis according to the following equation:
[tex]6CO_2 + 6H_2O ---> C_6H_1_2O_6 + 6O_2[/tex]
The process of photosynthesis takes place in 2 reactions:
- Light-dependent
- Light-independent
Oxygen is produced from the splitting of water in the light-dependent reaction. Hence, the production of oxygen stops when there is no light - when the sun sets.
Whatever quantity of oxygen that has been produced just before the sun sets would remain and will gradually be used for respiration by the Elodea plant until the sun rises again the following day.
Thus, the level of oxygen in the tube would usually be lowest just before the sun rises and oxygen can be produced again.
More on the light reaction of photosynthesis can be found here: https://brainly.com/question/14015819
